Multicentre international audit of IMACS malignancy screening guidelines in idiopathic inflammatory myopathies: insights from the myositis audit and research collaborative group

Background Consensus guidelines for malignancy screening in idiopathic inflammatory myopathy (IIM) were recently published by the International Myositis Assessment and Clinical Studies (IMACS) working group. This international multicentre study audited historical cancer screening practices against IMACS recommendations and examined the distribution of observed malignancies across IMACS-defined risk categories in a real-world cohort.

Methods This retrospective study included patients with IIM from eight centres across seven countries/regions. Patients were stratified using IMACS-defined cancer risk categories. Historical screening was compared with the guideline recommendations. Multivariable logistic regression identified predictors of cancer and underscreening.

Results Of the 795 patients (72.3% female), 51.7%, 37.9% and 10.4% were classified as high risk, moderate risk and standard risk, respectively. Across all sites, few high-risk (6.2%), moderate-risk (2.7%) and standard-risk (11.1%) patients underwent a full panel of IMACS-recommended tests. Within 3 years of diagnosis, 86 patients (10.8%) developed malignancy. Among observed cancers, 77.4% occurred in high-risk and 22.6% in moderate-risk patients, with none detected in the standard-risk group. Anti-transcription intermediary factor 1-gamma (TIF1γ) positivity (OR 4.64, 95% CI 2.35 to 9.16, p<0.001), smoking (OR 3.00, 95% CI 1.64 to 5.50, p<0.001), night sweats (OR 12.76, 95% CI 2.72 to 59.87, p=0.001) and increasing age (OR 1.05 95% CI 1.03 to 1.07 per year, p<0.001) were independently associated with cancer, whereas anti-Mi2 antibodies and non-dermatomyositis subtypes were protective. Cancer risk increased with each additional high-risk feature (OR 1.70) and decreased with each low-risk feature (OR 0.76). Underscreened individuals had lower rates of immune-mediated necrotising myopathy (5.6% vs 14.3%, p=0.005) and anti-TIF1γ positivity (6.8% vs 31.4%, p<0.001).

Conclusion Observed cancer distribution across IMACS risk categories was consistent with the framework’s stratification logic, but differential screening intensity precludes formal assessment of predictive validity. Variation between historical practice and current recommendations underscores the need for continued education and prospective longitudinal studies to assess cumulative risk, age thresholds, screening uptake and outcomes in real-world clinical settings.